Tablets are a common type of dosage form and various means for improving their properties have been tried. Current methods for coating tablets, such as pharmaceutical tablets include the using of acelacoaters or pan coaters, which spray low molecular weight HPMC grades onto tablets so imparting a surface layer, which is uniform and smooth, but opaque and of low gloss. It is possible for the tablets to have embossed lettering on them. This method of coating tablets is however very time consuming and requires a high level of expertise to produce satisfactory results. Production complications such as tablet twinning are common, where two tablets become attached to one another during the spray coating operation. In addition to these problems it is necessary to compact the tablets under relatively high pressures so that they do not disintegrate during the coating process. This high level of compaction can have an adverse effect on the disintegration and dissolution rates of active ingredients contained within the capsule, for example, leading to a delay in the release of a drug to a patient, whilst the tablet slowly dissolves in the stomach of the patient.
An alternative to spray or pan coating is to use two-piece hard capsules. These are produced by a dipping process, typically a HPMC solution is used, producing half shells which interlock and thus produce an enclosed capsule. These capsules are typically opaque but glossy, and cannot have any form of embossment, as this would interfere with the overlap interlocking process. The nature of the capsule dictates that there will always be an airspace above the powder fill level. Additionally, it is not possible to compact the powder into these tablets, and this so limits the quantity of powder which can be encapsulated. It follows that this lack of compaction can effectively reduce the amount of e.g. medicament which can be encapsulated. The existence of the air space in the capsule and lack of compaction of the powder contained within the capsule leads to a capsule that is inevitably larger than necessary.
It has also been found that, after manufacture and/or sale of two-piece hard capsules, the capsules can be easily and illegally interfered with, as it is possible to separate the two halves of the capsule and tamper with its contents and replace the two halves back together without there being any obvious change in the capsule's external appearance such to suggest to the user that there was anything wrong with the capsule. This means that it can be difficult to detect capsules which have had their contents tampered with.
HPMC and certain other non-gelatin materials are suitable for ingestion by humans, so delivery capsules with gelatin walls find potential use as ingestible capsules, e.g. for the delivery of accurately metered doses of pharmaceutical preparations and dietary supplements, as a possible replacement for gelatin based capsules. Conventional tablets have already been enrobed. See for example WO 02/098394.